Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite. The name comes from Greek mythology: Niobe, daughter of Tantalus.Sony VGP-BPL18 Battery
Niobium has physical and chemical properties similar to those of the element tantalum, and the two are therefore difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801, and named it columbium. In 1809, the English chemist William Hyde Wollaston wrongly concluded that tantalum and columbium were identical.Sony VGP-BPS18 Battery
The German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element (as distinguished from tantalum), and for a century both names were used interchangeably.Sony VGP-BPL20 Battery
The name of the element was officially adopted as niobium in 1949.
It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines.Sony VGP-BPS20/B Battery
Although alloys contain only a maximum of 0.1%, that small percentage of niobium improves the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet and rocket engines. Niobium is used in various superconducting materials.Sony VGP-BPS20/S Battery
These superconducting alloys, also containing titanium andtin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include its use in welding, nuclear industries, electronics, optics, numismatics and jewelry. In the last two applications, niobium's low toxicity and ability to be colored by anodization are particular advantages.Sony VGP-BPL21 Battery
Niobium was discovered by the English chemist Charles Hatchett in 1801.[1] He found a new element in a mineral sample that had been sent to England from Massachusetts, United States in 1734 by a John Winthrop,[2] and named the mineral columbite and the new element columbium after Columbia, the poetical name for America.Sony VGP-BPS21 Battery
The columbium discovered by Hatchett was probably a mixture of the new element with tantalum.
Subsequently, there was considerable confusion[4] over the difference between columbium (niobium) and the closely related tantalum.Sony VGP-BPS21/S Battery
In 1809, the English chemist William Hyde Wollaston compared the oxides derived from both columbium—columbite, with a density 5.918 g/cm3, and tantalum—tantalite, with a density over 8 g/cm3, and concluded that the two oxides, despite the significant difference in density, were identical; thus he kept the name tantalum.Sony VGP-BPS21A Battery
This conclusion was disputed in 1846 by the German chemist Heinrich Rose, who argued that there were two different elements in the tantalite sample, and named them after children of Tantalus: niobium (from Niobe), and pelopium (from Pelops).[5][6] This confusion arose from the minimal observed differences between tantalum and niobium.Sony VGP-BPS21A/B Battery
The claimed new elements pelopium, ilmenium anddianium[7] were in fact identical to niobium or mixtures of niobium and tantalum.[8]
The differences between tantalum and niobium were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand,and Henri Etienne Sainte-Claire Deville,Sony VGP-BPS21B Battery
as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865[8][9] and finally by the Swiss chemist Jean Charles Galissard de Marignac[10] in 1866, who all proved that there were only two elements. Articles on ilmeniumcontinued to appear until 1871.Sony VGP-BPL22 Battery
De Marignac was the first to prepare the metal in 1864, when he reduced niobium chloride by heating it in an atmosphere of hydrogen. Although de Marignac was able to produce tantalum-free niobium on a larger scale by 1866, it was not until the early 20th century that niobium was first used commercially, inincandescent lamp filaments.Sony VGP-BPS22 Battery
This use quickly became obsolete through the replacement of niobium withtungsten, which has a higher melting point and thus is preferable for use in incandescent lamps. The discovery that niobium improves the strength of steel was made in the 1920s, and this application remains its predominant use.Sony VGP-BPS22/A Battery
In 1961 the American physicist Eugene Kunzler and coworkers at Bell Labsdiscovered that niobium-tin continues to exhibit superconductivity in the presence of strong electric currents and magnetic fields, making it the first material to support the high currents and fields necessary for useful high-power magnets and electrically powered machinery.Sony VGP-BPS22A Battery
This discovery would allow — two decades later — the production of long multi-strand cables that could be wound into coils to create large, powerful electromagnets for rotating machinery, particle accelerators, or particle detectors.
Naming of the element
Columbium (symbol Cb ) was the name originally given to this element by Hatchett,Sony VGP-BPL23 Battery
and this name remained in use in American journals—the last paper published by American Chemical Society with columbium in its title dates from 1953[17]—while niobiumwas used in Europe. To end this confusion, the name niobium was chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam in 1949.Sony VGP-BPS23 Battery
A year later this name was officially adopted by the International Union of Pure and Applied Chemistry (IUPAC) after 100 years of controversy, despite the chronological precedence of the name Columbium.[18] The latter name is still sometimes used in US industry.Sony VGP-BPS23/B Battery
This was a compromise of sorts; the IUPAC accepted tungsteninstead of wolfram, in deference to North American usage; and niobium instead of columbium, in deference to European usage. Not everyone agreed, and while many leading chemical societies and government organizations refer to it by the official IUPAC name, many leading metallurgists, metal societies, and the United States Geological Survey still refer to the metal by the original "columbium".Sony VGP-BPS23/D Battery
Physical
Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table (see table), although it has an atypical configuration in its outermost electron shells compared to the rest of the members. (This can be observed in the neighborhood of ruthenium (44), rhodium (45), and palladium (46).)Sony VGP-BPS23/G Battery
| Z | Element | No. of electrons/shell |
| 23 | vanadium | 2, 8, 11, 2 |
| 41 | niobium | 2, 8, 18, 12, 1 |
| 73 | tantalum | 2, 8, 18, 32, 11, 2 |
| 105 | dubnium | 2, 8, 18, 32, 32, 11, 2 |
Niobium becomes a superconductor at cryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.2 K.[22]Niobium has the largest magnetic penetration depth of any element.Sony VGP-BPS23/P Battery
In addition, it is one of the three elemental Type II superconductors, along with vanadium andtechnetium. The superconductive properties are strongly dependent on the purity of the niobium metal.[23] When very pure, it is comparatively soft and ductile, but impurities make it harder.Sony VGP-BPS23/W Battery
The metal has a low capture cross-section for thermal neutrons;[25] thus it is used in the nuclear industries.[26]
Chemical
The metal takes on a bluish tinge when exposed to air at room temperature for extended periods.[27] Despite presenting a high melting point in elemental form (2,468 °C), it has a low density in comparison to other refractory metals.Sony Limited Edition 007 Battery
Furthermore, it is corrosion resistant, exhibits superconductivity properties, and forms dielectric oxide layers.
Niobium is slightly less electropositive and more compact than its predecessor in the periodic table, zirconium, whereas it is virtually identical in size to the heavier tantalum atoms, owing to the lanthanide contraction.Sony VAIO VGC-LB15 Battery
As a result, niobium's chemical properties are very similar to those for tantalum, which appears directly below niobium in the periodic table. Although its corrosion resistance is not as outstanding as that of tantalum, its lower price and greater availability make niobium attractive for less demanding uses such as linings in chemical plants.Sony VGN-AR Series Battery
Naturally occurring niobium is composed of one stable isotope, 93Nb.As of 2003, at least 32 radioisotopes have also been synthesized, ranging in atomic massfrom 81 to 113. The most stable of these is 92Nb with a half-life of 34.7 million years. One of the least stable is 113Nb, with an estimated half-life of 30 milliseconds.Sony VGN-CR Series Battery
Isotopes that are lighter than the stable 93Nb tend to decay by ?+ decay, and those that are heavier tend to decay by ?- decay, with some exceptions. 81Nb, 82Nb, and 84Nb have minor ?+ delayed proton emission decay paths, 91Nb decays by electron capture and positron emission, and 92Nb decays by both ?+and ?- decay.Sony VIAO VGN-G Series Battery
At least 25 nuclear isomers have been described, ranging in atomic mass from 84 to 104. Within this range, only 96Nb, 101Nb, and 103Nb do not have isomers. The most stable of niobium's isomers is 93mNb with a half-life of 16.13 years. The least stable isomer is 84mNb with a half-life of 103 ns.Sony VIAO VGN-G118 Battery
All of niobium's isomers decay byisomeric transition or beta decay except 92m1Nb, which has a minor electron capture decay chain.[28]
Occurrence
Niobium is estimated to be 33rd on the list of the most common elements in the Earth’s crust with 20 ppm.[Sony VIAO VGN-G118CN/B Battery
Some think that the abundance on Earth should be much greater, but that the “missing” niobium may be located in the Earth’s core due to the metal's high density.The free element is not found in nature, but it does occur in minerals.Minerals that contain niobium often also contain tantalum, such as columbite ((Fe,Mn)(Nb,Ta)2O6) and columbite-tantalite (or coltan, (Fe,Mn)(Ta,Nb)2O6).Sony VIAO VGN-G118CN/T Battery
Columbite-tantalite minerals are most usually found as accessory minerals in pegmatite intrusions, and in alkaline intrusive rocks. Less common are the niobates of calcium, uranium, thorium and the rare earth elements such as pyrochlore ((Na,Ca)2Nb2O6(OH,F)) and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6).Sony VIAO VGN-G218 Battery
These large deposits of niobium have been found associated with carbonatites (carbonate-silicate igneous rocks) and as a constituent of pyrochlore.[31]
The two largest deposits of pyrochlore were found in the 1950s in Brazil and Canada, and both countries are still the major producers of niobium mineral concentrates.Sony VGN-TZ121 Battery
The largest deposit is hosted within a carbonatite intrusion at Araxá, Minas Gerais Brazil, owned by CBMM (Companhia Brasileira de Metalurgia e Mineração); the other deposit is located at Goiás owned by Anglo American plc (through its subsidiary Mineração Catalão), also hosted within a carbonatite intrusion.Sony VGN-TZ13 Battery
Altogether these two Brazilian mines produce around 75% of world supply. The third largest producer of niobium is the carbonatite-hosted Niobec Mine,Saint-Honoré near Chicoutimi, Quebec owned by Iamgold Corporation Ltd, which produces around 7% of world supply.Sony VGN-TZ131 Battery
Extensive unexploited resources are located in Nigeria, Democratic Republic of Congo, Tanzania, Malawi, Australia, Afghanistan, Russia and Colombia.
Production
After the separation from the other minerals, the mixed oxides of tantalum Ta2O5 and niobium Nb2O5 are obtained. The first step in the processing is the reaction of the oxides with hydrofluoric acid:Sony VGN-TZ132N Battery
Ta2O5 + 14 HF ? 2 H2[TaF7] + 5 H2O
Nb2O5 + 10 HF ? 2 H2[NbOF5] + 3 H2O
The first industrial scale separation, developed by de Marignac, exploits the differing solubilities of the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate monohydrate (K2[NbOF5]·H2O) and dipotassium heptafluorotantalate (K2[TaF7]) in water.Sony VGN-TZ132/N Battery
Newer processes use the liquid extraction of the fluorides from aqueoussolution by organic solvents like cyclohexanone. The complex niobium and tantalum fluorides are extracted separately from the organic solvent with water and either precipitated by the addition of potassium fluoride to produce a potassium fluoride complex, or precipitated with ammonia as the pentoxide:Sony VGN-TZ17N Battery
H2[NbOF5] + 2 KF ? K2[NbOF5]? + 2 HF
Followed by:
2 H2[NbOF5] + 10 NH4OH ? Nb2O5? + 10 NH4F + 7 H2O
Several methods are used for the reduction to metallic niobium. The electrolysis of a molten mixture of K2[NbOF5] and sodium chloride is one;Sony VGN-TZ16N Battery
the other is the reduction of the fluoride with sodium. With this method niobium with a relatively high purity can be obtained. In large scale production the reduction of Nb2O5 with hydrogen or carbon is used. In the process involving the aluminothermic reaction a mixture of iron oxide and niobium oxide is reacted with aluminium:Sony VGN-TZ18N Battery
3 Nb2O5 + Fe2O3 + 12 Al ? 6 Nb + 2 Fe + 6 Al2O3
To enhance the reaction, small amounts of oxidizers like sodium nitrate are added. The result is aluminium oxide and ferroniobium, an alloy of iron and niobium used in the steel production. The ferroniobium contains between 60 and 70% of niobium.Sony VAIO VGN-AR47G/E1 Battery
Without addition of iron oxide, aluminothermic process is used for the production of niobium. Further purification is necessary to reach the grade for superconductive alloys. Electron beam melting under vacuum is the method used by the two major distributors of niobium. Sony VAIO VGN-AR520E Battery
The United States Geological Survey estimates that the production increased from 38,700 tonnes in 2005 to 44,500 tonnes in 2006. The worldwide resources are estimated to be 4,400,000 tonnes.During the ten-year period between 1995 and 2005, the production more than doubled, starting from 17,800 tonnes in 1995.Sony VAIO VGN-AR53DB Battery
Compounds
Niobium is in many ways similar to tantalum and zirconium. It reacts with most nonmetals at high temperatures: niobium reacts with fluorine at room temperature, withchlorine and hydrogen at 200 °C, and with nitrogen at 400 °C, giving products that are frequently interstitial and nonstoichiometric.Sony VAIO VGN-AR54DB Battery
The metal begins tooxidize in air at 200 °C, and is resistant to corrosion by fused alkalis and by acids, including aqua regia, hydrochloric, sulfuric, nitric and phosphoric acids. Niobium is attacked by hydrofluoric acid and hydrofluoric/nitric acid mixtures.Sony VAIO VGN-AR550E Battery
Although niobium exhibits all of the formal oxidation states from +5 to -1, in most commonly encountered compounds, it is found in the +5 state.[24]Characteristically, compounds in oxidation states less than 5+ display Nb-Nb bonding.
Oxides and sulfides
Niobium forms oxides with the oxidation states +5 (Nb2O5), +4 (NbO2), and +3 (Nb2O3),Sony VAIO VGN-AR55DB Battery
as well as with the rarer oxidation state +2 (NbO).[41] Most commonly encountered is the pentoxide, precursor to almost all niobium compounds and alloys. Niobates are generated by dissolving the pentoxide in basic hydroxidesolutions or by melting it in alkali metal oxides. Examples are lithium niobate (LiNbO3) and lanthanum niobate (LaNbO4).Sony VAIO VGN-AR630E Battery
In the lithium niobate is a trigonally distorted perovskite-like structure, whereas the lanthanum niobate contains lone NbO43?ions.[33] The layered niobium sulfide (NbS2) is also known.
Halides
Niobium forms halides in the oxidation states of +5 and +4 as well as diverse substoichiometric compounds.Sony VAIO VGN-AR64DB Battery
The pentahalides (NbX5) feature octahedral Nb centres. Niobium pentafluoride (NbF5) is a white solid with a melting point of 79.0 °C and niobium pentachloride (NbCl5) is yellow (see image at left) with a melting point of 203.4 °C. Both are hydrolyzed to give oxides and oxyhalides, such as NbOCl3.Sony VAIO VGN-AR65DB Battery
The pentachloride is a versatile reagent being used to generate the organometallic compounds, such asniobocene dichloride ((C5H5)2NbCl2).[43] The tetrahalides (NbX4) are dark-coloured polymers with Nb-Nb bonds, for example the blackhygroscopic niobium tetrafluoride (NbF4) and brown niobium tetrachloride (NbCl4).Sony VAIO VGN-AR660U Battery
Anionic halide compounds of niobium are well known, owing in part to the Lewis acidity of the pentahalides. The most important is [NbF7]2-, which is an intermediate in the separation of Nb and Ta from the ores. This heptafluoride tends to form the oxopentafluoride more readily than does the tantalum compound.Sony VAIO VGN-AR690U Battery
Other halide complexes include octahedral [NbCl6]-:
Nb2Cl10 + 2 Cl- ? 2 [NbCl6]-
As for other early metals, a variety of reduced halide clusters are known, the premier example being [Nb6Cl18]4-.Sony VAIO VGN-AR71ZU Battery
Nitrides and carbides
Other binary compounds of niobium include the niobium nitride (NbN), which becomes a superconductor at low temperatures and is used in detectors for infrared light. The main niobium carbide is NbC, an extremely hard, refractory, ceramic material, commercially used intool bits for cutting tools.Sony VAIO VGN-AR730E/B Battery
Applications
It is estimated that out of 44,500 metric tons of niobium mined in 2006, 90% was used in the production of high-grade structural steel, followed by its use in superalloys. The use of niobium alloys for superconductors and in electronic components account only for a small share of the production.Sony VAIO VGN-AR73DB Battery
Steel production
Niobium is an effective microalloying element for steel. Adding niobium to the steel causes the formation of niobium carbide andniobium nitride within the structure of the steel. These compounds improve the grain refining, retardation of recrystallization, and precipitation hardening of the steel.Sony VAIO VGN-AR74DB Battery
These effects in turn increase the toughness, strength, formability, and weldability of the microalloyed steel.Microalloyed stainless steels have a niobium content of less than 0.1%. It is an important alloy addition to high strength low alloy steels which are widely used as structural components in modern automobiles.Sony VAIO VGN-AR75UDB Battery
These niobium-containing alloys are strong and are often used in pipeline construction.
Superalloys
Appreciable amounts of the element, either in its pure form or in the form of high-purity ferroniobium and nickel niobium,Sony VAIO VGN-AR790U/B Battery
are used in nickel-, cobalt-, and iron-based superalloys for such applications as jet engine components, gas turbines, rocket subassemblies, and heat resisting and combustion equipment. Niobium precipitates a hardening ?''-phase within the grain structure of the superalloy.Sony VAIO VGN-AR820E Battery
The alloys contain up to 6.5% niobium. One example of a nickel-based niobium-containing superalloy is Inconel 718, which consists of roughly 50% nickel, 18.6% chromium, 18.5% iron, 5% niobium, 3.1% molybdenum, 0.9%titanium, and 0.4% aluminium.These superalloys are used, for example, in advanced air frame systems such as those used in the Gemini program.Sony VAIO VGN-AR830E Battery
An alloy used for liquid rocket thruster nozzles, such as in the main engine of the Apollo Lunar Modules, is C103, which consists of 89% niobium, 10% hafnium and 1% titanium. Another niobium alloy was used for the nozzle of the Apollo Service Module.Sony VAIO VGN-AR83S Battery
As niobium is oxidized at temperatures above 400 °C, a protective coating is necessary for these applications to prevent the alloy from becoming brittle.
Superconducting magnets
Niobium-germanium (Nb3Ge), niobium-tin (Nb3Sn), as well as the niobium-titanium alloys are used as a type II superconductor wire for superconducting magnets.Sony VAIO VGN-AR83US Battery
These superconducting magnets are used in magnetic resonance imaging and nuclear magnetic resonance instruments as well as in particle accelerators.For example, the Large Hadron Collider uses 600 tons of superconducting strands, while the International Thermonuclear Experimental Reactor is estimated to use 600 tonnes of Nb3Sn strands and 250 tonnes of NbTi strands.Sony VAIO VGN-AR84S Battery
In 1992 alone, niobium-titanium wires were used to construct more than US$1 billion worth of clinical magnetic resonance imaging systems.
Superconducting, other
The Superconducting Radio Frequency (RF) cavities used in the free electron lasers TESLA and XFEL are made from pure niobium.Sony VAIO VGN-AR84US Battery
The high sensitivity of superconducting niobium nitride bolometers make them an ideal detector for electromagnetic radiation in the THz frequency band. These detectors were tested at the Heinrich Hertz Submillimeter Telescope, the South Pole Telescope, theReceiver Lab Telescope, and at APEX and are now used in the HIFI instrument on board the Herschel Space Observatory.Sony VAIO VGN-AR85S Battery
Electroceramics
Lithium niobate, which is a ferroelectric, is used extensively in mobile telephones and optical modulators, and for the manufacture of surface acoustic wave devices. It belongs to the ABO3 structure ferroelectrics like lithium tantalate and barium titanate.Sony VAIO VGN-AR85US Battery
Niobium was evaluated as a cheaper alternative to tantalum incapacitors, but tantalum capacitors are still predominant. Niobium is added to glass in order to attain a higher refractive index, a property of use to the optical industry in making thinner corrective glasses.Sony VAIO VGN-AR870EA Battery
Hypoallergenic applications: medicine and jewelry
Niobium and some niobium alloys are physiologically inert and thus hypoallergenic. For this reason, niobium is found in many medical devices such as pacemakers.[62]Niobium treated with sodium hydroxide forms a porous layer that aids osseointegration.Sony VAIO VGN-AR890U Battery
Along with titanium, tantalum, and aluminium, niobium can also be electrically heated and anodized, resulting in a wide array of colours using a process known as reactive metal anodizing which is useful in making jewelry. The fact that niobium is hypoallergenic also benefits its use in jewelry.Sony VAIO VGN-AR93S Battery
Numismatics
Niobium is used as a precious metal in commemorative coins, often with silver or gold. For example, Austria produced a series of silver niobium euro coins starting in 2003; the colour in these coins is created by the diffraction of light by a thin oxide layer produced by anodising.Sony VAIO VGN-AR93US Battery
In 2008, six coins are available showing a broad variety of colours in the centre of the coin: blue, green, brown, purple, violet, or yellow. Two more examples are the 2004 Austrian €25 150 Years Semmering Alpine Railway commemorative coin, and the 2006 Austrian €25 European Satellite Navigation commemorative coin.Sony VAIO VGN-AR94S Battery
Latvia produced a similar series of coins starting in 2004, with one following in 2007. In 2011, the Royal Canadian Mint started production of a $5 sterling silver and niobium coin named Hunter's Moon in which the niobium was selectively oxidized, thus creating unique finishes where no two coins are exactly alike.Sony VAIO VGN-AR94US Battery
Other
The arc-tube seals of high pressure sodium vapor lamps are made from niobium, or niobium with 1% of zirconium, because niobium has a very similar coefficient of thermal expansion to the sintered alumina arc tube ceramic, a translucent material which resists chemical attack or reduction by the hot liquid sodium and sodium vapour contained inside the operating lamp.Sony VAIO VGN-AR95S Battery
The metal is also used in arc welding rods for some stabilized grades of stainless steel.
Precautions
Niobium has no known biological role. While niobium dust is an eye and skin irritant and a potential fire hazard, elemental niobium on a larger scale is physiologically inert (and thus hypoallergenic) and harmless. Sony VAIO VGN-AR95US Battery
It is frequently used in jewelry and has been tested for use in some medical implants.
Niobium-containing compounds are rarely encountered by most people, but some are toxic and should be treated with care. The short and long term exposure to niobates and niobium chloride, two chemicals that are water soluble, have been tested in rats.Sony VAIO VGN-AW110J/H Battery
Rats treated with a single injection of niobium pentachloride or niobates show a median lethal dose (LD50) between 10 and 100 mg/kg. For oral administration the toxicity is lower; a study with rats yielded a LD50 after seven days of 940 mg/kg.Sony VAIO VGN-AW11M/H Battery
Molybdenum is a Group 6 chemical element with the symbol Moand atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek ???????? molybdos, meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages,[3] since its ores were confused with lead ores.Sony VAIO VGN-AW11S/B Battery
The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Molybdenum does not occur as a free metal on Earth, but rather in various oxidation states in minerals.Sony VAIO VGN-AW11XU/Q Battery
Industrially, molybdenum compounds are used in high-pressure and high-temperature applications, as pigments and catalysts.
Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 byPeter Jacob Hjelm.Sony VAIO VGN-AW11Z/B Battery
Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42? is soluble and forms when molybdenum-containing minerals are in contact with oxygen and water.
Molybdenum-containing enzymes are used as catalysts by some bacteria to break the chemical bond in atmospheric molecularnitrogen, allowing biological nitrogen fixation.Sony VAIO VGN-AW120J/H Battery
At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Owing to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms (eukaryotes), though not in all bacteria.Sony VAIO VGN-AW150Y/H Battery
Physical properties
In its pure form, molybdenum is a silvery-white metal with a Mohs hardness of 5.5. It has a melting point of 2,623 °C(4,753 °F); of the naturally occurring elements, only tantalum, osmium, rhenium, tungsten, and carbon have higher melting points.Sony VAIO VGN-AW160J/Q Battery
Molybdenum burns only at temperatures above 600 °C (1,112 °F).[5] It has one of the lowest coefficients ofthermal expansion among commercially used metals.[6] The tensile strength of molybdenum wires increases about 3 times, from about 10 to 30 GPa, when their diameter decreases from ~50–100 nm to 10 nm.Sony VAIO VGN-AW170Y/Q Battery
There are 35 known isotopes of molybdenum, ranging in atomic mass from 83 to 117, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, only molybdenum-100 is unstable.Sony VAIO VGN-AW180Y/Q Battery
All unstable isotopes of molybdenum decay into isotopes of niobium,technetium, and ruthenium.
Molybdenum-98 is the most abundant isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a half-life of about 1019 y and undergoes double beta decay into ruthenium-100.Sony VAIO VGN-AW190JAH Battery
Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns.
As also noted below, the most common isotopic molybdenum application involves molybdenum-99, which is a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m, a nuclear isomer used in various imaging applications in medicine.Sony VAIO VGN-AW190NAB Battery
In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of technetium-99
Compounds and chemistry
Molybdenum is a transition metal with an electronegativity of 1.8 on the Pauling scale and an atomic mass of 95.94 g/mol.Sony VAIO VGN-AW190NBB Battery
It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 790 °C, resulting inmolybdenum trioxide:
2 Mo + 3 O2 ? 2 MoO3
The trioxide is volatile and sublimates at high temperatures. Sony VAIO VGN-AW190NCB Battery
This prevents formation of a continuous protective oxide layer, which would stop the bulk oxidation of metal. Molybdenum has several oxidation states, the most stable being +4 and +6 (bolded in the table). The chemistry and the compounds show more similarity to those of tungsten than that of chromium.Sony VAIO VGN-AW190YAB Battery
An example is the instability of molybdenum(III) and tungsten(III) compounds as compared with the stability of the chromium(III) compounds. The highest oxidation state is common in themolybdenum(VI) oxide (MoO3), whereas the normal sulfur compound is molybdenum disulfide MoS2.Sony VAIO VGN-AW190YBB Battery
Molybdenum(VI) oxide is soluble in strong alkaline water, forming molybdates (MoO42?). Molybdates are weaker oxidants than chromates, but they show a similar tendency to form complex oxyanions by condensation at lower pH values, such as [Mo7O24]6? and [Mo8O26]4?.Sony VAIO VGN-AW190YCB Battery
Polymolybdates can incorporate other ions into their structure, forming polyoxometalates.[15] The dark-blue phosphorus-containing heteropolymolybdate P[Mo12O40]3? is used for thespectroscopic detection of phosphorus.[16] The broad range of oxidation states of molybdenum is reflected in various molybdenum chlorides:Sony VAIO VGN-AW190YDB Battery
- Molybdenum(II) chloride MoCl2 (yellow solid)
- Molybdenum(III) chloride MoCl3 (dark red solid)
- Molybdenum(IV) chloride MoCl4 (black solid)
- Molybdenum(V) chloride MoCl5 (dark green solid)
- Molybdenum(VI) chloride MoCl6 (brown solid)
The structure of the MoCl2 is composed of Mo6Cl84+ clusters with four chloride ions to compensate the charge.Sony VAIO VGN-AW220J/B Battery
Like chromium and some other transition metals, molybdenum is able to form quadruple bonds, such as in Mo2(CH3COO)4. This compound can be transformed into Mo2Cl84?, which also has a quadruple bond.
The oxidation state 0 is possible with carbon monoxide as ligand, such as in molybdenum hexacarbonyl, Mo(CO)6.Sony VAIO VGN-AW230J/H Battery
Molybdenite—the principal ore from which molybdenum is now extracted—was previously known as molybdena. Molybdena was confused with and often implemented as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant.Sony VAIO VGN-AW235J/B Battery
Even when molybdena was distinguishable from graphite, it was still confused with a common leadore (now called galena), which took its name from Ancient Greek ???????? molybdos, meaning lead. Although apparent deliberate alloying of molybdenum with steel in one 14th-century Japanese sword (mfd. ca. 1330) has been reported,Sony VAIO VGN-AW290JFQ Battery
that art was never employed widely and was later lost. In 1754, Bengt Andersson Qvist examined molybdenite and determined that it did not contain lead and was thus not the same as galena.
It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead.Sony VAIO VGN-AW41JF Battery
He and other chemists then correctly assumed that it was the ore of a distinct new element, named molybdenumfor the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.
For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of the metallurgical subfield.Sony VAIO VGN-AW41JF/H Battery
Early molybdenum steel alloys showed great promise in their increased hardness, but efforts were hampered by inconsistent results and a tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile,Sony VAIO VGN-AW41MF Battery
leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that molybdenum be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process to recover molybdenite from ores; flotation remains the primary isolation process.Sony VAIO VGN-AW41MF/H Battery
During the first World War, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high speed steels. Some British tanks were protected by 75 mm (3 in) manganese steel plating, but this proved to be ineffective.Sony VAIO VGN-AW41XH Battery
The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection. After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications.Sony VAIO VGN-AW41XH/Q Battery
In World War II, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.
Occurrence
The world's largest producers of molybdenum materials are the United States, China, Chile, Peruand Canada.Sony VAIO VGN-AW41ZF Battery
Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.Sony VAIO VGN-AW41ZF/B Battery
Large mines in Colorado (such as the Henderson mine and the now-inactiveClimax mine) and in British Columbia yield molybdenite as their primary product, while manyporphyry copper deposits such as the Bingham Canyon Mine in Utah and the Chuquicamata mine in northern Chile produce molybdenum as a byproduct of copper mining.Sony VAIO VGN-AW50DB/H Battery
The Knaben mine in southern Norway was opened in 1885, making it the first molybdenum mine. It remained open until 1973.
Molybdenum is the 54th most abundant element in the Earth's crust and the 25th most abundant element in the oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe.Sony VAIO VGN-AW51JGB Battery
The Russian Luna 24 mission discovered a molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene fragment taken from Mare Crisium on the Moon.
Production
In molybdenite processing, the molybdenite is first heated to a temperature of 700 °C (1,292 °F) and the sulfide is oxidized into molybdenum(VI) oxide by air:Sony VAIO VGN-AW52JGB Battery
2 MoS2 + 7 O2 ? 2 MoO3 + 4 SO2
The oxidized ore is then either heated to 1,100 °C (2,010 °F) to sublimate the oxide, or leached with ammonia which reacts with the molybdenum(VI) oxide to form water-soluble molybdates:
MoO3 + 2 NH4OH ? (NH4)2(MoO4) + H2O
Copper, an impurity in molybdenite, is less soluble in ammonia. To completely remove it from the solution, it is precipitated with hydrogen sulfide.Sony VAIO VGN-AW53FB Battery
Pure molybdenum is produced by reduction of the oxide with hydrogen, while the molybdenum for steel production is reduced by the aluminothermic reaction with addition of iron to produce ferromolybdenum. A common form of ferromolybdenum contains 60% molybdenum.Sony VAIO VGN-AW70B/Q Battery
Molybdenum has a value of approximately $30,000 per tonne as of August 2009. It maintained a price at or near $10,000 per tonne from 1997 through 2003, and reached, due to increased demand, a peak of $103,000 per tonne in June 2005. In 2008 the London Metal Exchange announced that molybdenum would be traded as a commodity on the exchange.Sony VAIO VGN-AW71JB Battery
Applications
The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening makes it useful in applications that involve intense heat, including the manufacture of armour, aircraft parts, electrical contacts, industrial motors and filaments.Sony VAIO VGN-AW72JB Battery
Most high-strength steel alloys (example 41xx steels) contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steels, tool steels, cast irons and high-temperature superalloys.Sony VAIO VGN-AW73FB Battery
Molybdenum is also used in steel alloys for its high corrosion resistance and weldability. Molybdenum contributes further corrosion resistance to "chrome-moly" type-300 stainless steels (high-chromium steels that are corrosion-resistant already due to their chromium content) and especially so in the so-called superaustenitic stainless steels (such as alloy AL-6XN).Sony VAIO VGN-AW80NS Battery
Molybdenum acts by increasing lattice strain, thus increasing the energy required to dissolve out iron atoms from the surface.
Because of its lower density and more stable price, molybdenum is sometimes used instead of tungsten. An example is the 'M' series of high-speed steels such as M2, M4 and M42 as substitution for the 'T' steel series which contain tungsten.Sony VAIO VGN-AW80S Battery
Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2,623 °C (4,753 °F), molybdenum rapidly oxidizes at temperatures above 760 °C (1,400 °F) making it better-suited for use in vacuum environments.Sony VAIO VGN-AW80US Battery
TZM (Mo (~99%), Ti (~0.5%), Zr (~0.08%) and some C) is a corrosion-resisting molybdenum superalloy that resists molten fluoride salts at temperatures above 1300C. It has about twice the strength of pure Mo, and is more ductile and more weldable, yet in tests it resisted corrosion of a standard eutectic salt (FLiBe) and salt vapors used in molten salt reactors for 1100 hours with so little corrosion that it was difficult to measure.Sony VAIO VGN-AW81DS Battery
Other molybdenum-based alloys which do not contain iron have only limited applications. For example, because of the corrosion resistance against molten zinc, both pure molybdenum and the molybdenum/tungsten alloy (70%/30%) are used for piping, stirrers and pump impellers which come into contact with molten zinc.Sony VAIO VGN-AW81JS Battery
Other applications as catalyst and compounds
- Molybdenum-99 is a parent radioisotope to the daughter radioisotope technetium-99m, which is used in many medical procedures.
- Molybdenum disulfide (MoS2) is used as a solid lubricant and a high-pressure high-temperature (HPHT) antiwear agent.Sony VAIO VGN-AW81YS Battery
- It forms strong films on metallic surfaces and is a common additive to HPHT greases—in case of a catastrophic grease failure, thin layer of molybdenum prevents contact of the lubricated parts. It also has semiconducting properties with distinct advantages over traditional silicon or graphene in electronics applications.Sony VAIO VGN-AW82DS Battery
- MoS2 is also used as a catalyst in hydrocracking of petroleum fractions which contain nitrogen, sulfur and oxygen.
- Molybdenum disilicide (MoSi2) is an electrically conducting ceramic with primary use in heating elements operating at temperatures above 1500 °C in air.Sony VAIO VGN-AW82JS Battery
- Molybdenum trioxide (MoO3) is used as an adhesive between enamels and metals. Lead molybdate (wulfenite) co-precipitated with lead chromate and lead sulfate is a bright-orange pigment used with ceramics and plastics.
- Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.Sony VAIO VGN-AW82YS Battery
- The element is also used in NO, NO2, NOx analyzers in power plants for pollution controls. At 350 °C (662 °F) the element acts as a catalyst for NO2/NOx to form only NO molecules for consistent readings by infrared light.
- Ammonium heptamolybdate is used in biological staining procedures.Sony VAIO VGN-AW83FS Battery
Biochemistry
The most important role of the molybdenum in living organisms is as a metal heteroatom at the active site in certain enzymes. In nitrogen fixation in certain bacteria, the nitrogenase enzyme,Sony VAIO VGN-AW83GS Battery
which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is also known). The structure of the catalytic center of the enzyme is similar to that in iron-sulfur proteins: it incorporates a Fe4S3 and multiple MoFe3S3 clusters.Sony VAIO VGN-AW83HS Battery
n 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor for nearly two billion years in the further evolution of eukaryotic life (which includes all plants and animals) as eukaryotes cannot fix nitrogen, and must therefore acquire most of their organic nitrogen from prokaryotic bacteria.Sony VAIO VGN-AW90NS Battery
The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. However, once oxygen dissolved in seawater it helped dissolve molybdenum from minerals on the sea bottom, making it available to nitrogen-fixing bacteria and allowing them to provide more nitrogen for higher forms of life.Sony VAIO VGN-AW90S Battery
Although oxygen once promoted nitrogen fixation via making molybdenum available in water, it also directly poisons nitrogenase enzymes, so that historically, after oxygen arrived in large quantities in Earth's air and water, organisms which continued to fix nitrogen in aerobic conditions were required to isolate their nitrogen-fixing enzymes in heterocysts, or similar structures which protect them from too much oxygen.Sony VAIO VGN-AW90US Battery
Though molybdenum forms compounds with various organic molecules, including carbohydrates and amino acids, it is transported throughout the human body as MoO42?. At least 50 molybdenum-containing enzymes were known by 2002, mostly in bacteria, and their number is increasing with every year;Sony VAIO VGN-AW91CDS Battery
those enzymes include aldehyde oxidase, sulfite oxidase and xanthine oxidase.I some animals, and in humans, the oxidation of xanthine to uric acid, a process of purine catabolism, is catalyzed by xanthine oxidase, a molybdenum-containing enzyme.Sony VAIO VGN-AW91CJS Battery
The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect protein synthesis, metabolism and growth.Sony VAIO VGN-AW91CYS Battery
In animals and plants these enzymes use molybdenum bound at the active site in a tricyclic molybdenum cofactor. All molybdenum-using enzymes so far identified in nature use this cofactor, save for the phylogenetically ancient molybdenum nitrogenases, which fix nitrogen in some bacteria and cyanobacteria.Sony VAIO VGN-AW91DS Battery
Molybdenum enzymes in plants and animals catalyze the oxidation and sometimes reduction of certain small molecules, as part of the regulation of nitrogen, sulfur and carbon cycles.
Human dietary intake and deficiency
The human body contains about 0.07 mg of molybdenum per kilogram of weight.Sony VAIO VGN-AW91JS Battery
It occurs in higher concentrations in the liver and kidneys and in lower concentrations in the vertebrae. Molybdenum is also present within human tooth enamel and may help prevent its decay.
The average daily intake of molybdenum varies between 0.12 and 0.24 mg, but it depends on the molybdenum content of the food.Sony VAIO VGN-AW91YS Battery
Pork, lamb and beef liver each have approximately 1.5 parts per million of molybdenum. Other significant dietary sources include green beans, eggs, sunflower seeds, wheat flour, lentils, cucumbers and cereal grain. Acute toxicity has not been seen in humans, and the toxicity depends strongly on the chemical state.Sony VAIO VGN-AW92CDS Battery
Studies on rats show a median lethal dose(LD50) as low as 180 mg/kg for some Mo compounds. Although human toxicity data is unavailable, animal studies have shown that chronic ingestion of more than 10 mg/day of molybdenum can cause diarrhea, growth retardation, infertility, low birth weight and gout; it can also affect the lungs, kidneys and liver.Sony VAIO VGN-AW92CJS Battery
Sodium tungstate is a competitive inhibitor of molybdenum. Dietary tungsten reduces the concentration of molybdenum in tissues.
Dietary molybdenum deficiency from low soil concentration of molybdenum has been associated with increased rates of esophageal cancer in a geographical band fromnorthern China to Iran.Sony VAIO VGN-AW92CYS Battery
Compared to the United States, which has a greater supply of molybdenum in the soil, people living in these areas have about 16 times greater risk for esophageal squamous cell carcinoma.
Molybdenum deficiency has also been reported as a consequence of non-molybdenum supplemented total parenteral nutrition (complete intravenous feeding) for long periods of time.Sony VAIO VGN-AW92DS Battery
It results in high blood levels of sulfite and urate, in much the same way as molybdenum cofactor deficiency. However, presumably since pure molybdenum deficiency from this mechanism is seen primarily in adults, the neurological consequences have not been as marked as for the congenital cofactor deficiency.Sony VAIO VGN-AW92JS Battery
Related diseases
A congenital molybdenum cofactor deficiency disease, seen in infants, results in interference with the ability of the body to use molybdenum in enzymes. It causes high levels of sulphite and urate, and neurological damage.Sony VAIO VGN-AW92YS Battery
The cause is the inability of the body to synthesize molybdenum cofactor, a heterocyclic molecule which binds molybdenum at the active site in all known human enzymes which use molybdenum.
Copper-molybdenum antagonism
High levels of molybdenum can interfere with the body's uptake of copper, producing copper deficiency.Sony VAIO VGN-AW93FS Battery
Molybdenum prevents plasma proteins from binding to copper, and it also increases the amount of copper that is excreted in urine. Ruminants that consume high amounts of molybdenum develop symptoms including diarrhea, stunted growth, anemia and achromotrichia (loss of hair pigment).Sony VAIO VGN-AW93GS Battery
These symptoms can be alleviated by the administration of more copper into the system, both in dietary form and by injection. The condition, as an effective copper deficiency, can be aggravated by excess sulfur.
Copper reduction or deficiency can also be deliberately induced for therapeutic purposes by the compound ammonium tetrathiomolybdate,Sony VAIO VGN-AW93HS Battery
in which the bright red aniontetrathiomolybdate is the copper-chelating agent. Tetrathiomolybdate was first used therapeutically in the treatment of copper toxicosis in animals. It was then introduced as a treatment in Wilson's disease, a hereditary copper metabolism disorder in humans;Sony VAIO VGN-AW93ZFS Battery
it acts both by competing with copper absorption in the bowel and by increasing excretion. It has also been found to have an inhibitory effect on angiogenesis, potentially via the inhibition of copper ion dependent membrane translocation process invovling a non-classical secretion pathway.Sony VAIO VGN-AW93ZGS Battery
This makes it an interesting investigatory treatment for cancer, age-related macular degeneration, and other diseases featuring excessive blood vessel deposition.
Precautions
Molybdenum dusts and fumes, which can be generated by mining or metalworking, can be toxic, especially if ingested (including dust trapped in the sinuses and later swallowed).Sony VAIO VGN-AW93ZHS Battery
Low levels of prolonged exposure can cause irritation to the eyes and skin. Direct inhalation or ingestion of molybdenum and its oxides should be avoided. OSHA regulations specify the maximum permissible molybdenum exposure in an 8-hour day as 5 mg/m3. Chronic exposure to 60 to 600 mg/m3 can cause symptoms including fatigue, headaches and joint pains.Sony VAIO VGN-BZ11EN Battery
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowestatomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature.Sony VAIO VGN-BZ11MN Battery
Naturally occurring technetium occurs as a spontaneous fission product in uranium ore or by neutron capture in molybdenum ores. The chemical properties of this silvery gray, crystallinetransition metal are intermediate between rhenium and manganese.
Many of technetium's properties were predicted by Dmitri Mendeleev before the element was discovered.Sony VAIO VGN-BZ11XN Battery
Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em). In 1937 technetium (specifically the technetium-97 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek ????????, meaning "artificial").Sony VAIO VGN-BZ12VN Battery
Its short-lived gamma ray-emitting nuclear isomer—technetium-99m—is used in nuclear medicine for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by-products of fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods.Sony VAIO VGN-BZ12XN Battery
Because no isotope of technetium has a half-life longer than 4.2 million years (technetium-98), its detection in red giants in 1952, which are billions of years old, helped bolster the theory that stars can produce heavier elements.
Search for element 43
From the 1860s through 1871, early forms of the periodic table proposed by Dimitri Mendeleev contained a gap betweenmolybdenum (element 42) and ruthenium (element 44).Sony VAIO VGN-BZ31VT Battery
In 1871, Mendeleev predicted this missing element would occupy the empty place below manganese and therefore have similar chemical properties. Mendeleev gave it the provisional name ekamanganese(from eka-, the Sanskrit word for one), because the predicted element was one place down from the known element manganese.Sony VAIO VGN-BZ31XT Battery
Many early researchers, both before and after the periodic table was published, were eager to be the first to discover and name the missing element; its location in the table suggested that it should be easier to find than other undiscovered elements. It was first thought to have been found in platinum ores in 1828 and was given the name polinium, but turned out to be impure iridium.Sony VAIO VGN-BZ560 Battery
Then, in 1846, the element ilmenium was claimed to have been discovered, but later was determined to be impure niobium. This mistake was repeated in 1847 with the "discovery" of pelopium.
In 1877, the Russian chemist Serge Kern reported discovering the missing element in platinum ore.Sony VAIO VGN-BZ560N24 Battery
Kern named what he thought was the new element davyum (after the noted English chemist Sir Humphry Davy), but it was eventually determined to be a mixture of iridium, rhodium and iron. Another candidate, lucium, followed in 1896, but it was determined to be yttrium.Sony VAIO VGN-BZ560N30 Battery
Then in 1908, the Japanese chemist Masataka Ogawa found evidence in the mineral thorianite, which he thought indicated the presence of element 43. Ogawa named the element nipponium, after Japan (which is Nippon in Japanese). In 2004, H. K Yoshihara used "a record of X-ray spectrum of Ogawa's nipponium sample from thorianite [which] was contained in a photographic plate preserved by his family.Sony VAIO VGN-BZ560P Battery
The spectrum was read and indicated the absence of the element 43 and the presence of the element 75 (rhenium)."
German chemists Walter Noddack, Otto Berg, and Ida Tacke reported the discovery of element 75 and element 43 in 1925, and named element 43 masurium Sony VAIO VGN-BZ560P20 Battery
(after Masuria in eastern Prussia, now in Poland, the region where Walter Noddack's family originated).[6] The group bombarded columbite with a beam of electrons and deduced element 43 was present by examining X-raydiffraction spectrograms.
Sony VAIO VGN-BZ560P22 Battery
The wavelength of the X-rays produced is related to the atomic number by a formula derived byHenry Moseley in 1913. The team claimed to detect a faint X-ray signal at a wavelength produced by element 43. Later experimenters could not replicate the discovery, and it was dismissed as an error for many years.Sony VAIO VGN-BZ560P28 Battery
Still, in 1933, a series of articles on the discovery of elements quoted the name masurium for element 43. Debate still exists as to whether the 1925 team actually did discover element 43.
Official discovery and later history
The discovery of element 43 was finally confirmed in a December 1936 experiment at the University of Palermo in Sicily conducted by Carlo Perrier and Emilio Segrè.Sony VAIO VGN-BZ560P30 Battery
In mid-1936, Segrè visited the United States, first Columbia University in New York and then the Lawrence Berkeley National Laboratory in California. He persuaded cyclotron inventor Ernest Lawrence to let him take back some discarded cyclotron parts that had become radioactive.Sony VAIO VGN-BZ560P34 Battery
Lawrence mailed him a molybdenum foil that had been part of the deflector in the cyclotron.
Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, that the molybdenum activity was indeed Z = 43. They succeeded in isolating the isotopes technetium-95 and technetium-97.Sony VAIO VGN-BZ561 Battery
University of Palermo officials wanted them to name their discovery "panormium", after the Latin name for Palermo, Panormus. In 1947 element 43 was named after the Greek word ????????, meaning "artificial", since it was the first element to be artificially produced.Sony VAIO VGN-BZ561N20 Battery
Segrè returned to Berkeley and met Glenn T. Seaborg. They isolated the metastable isotope technetium-99m, which is now used in some ten million medical diagnostic procedures annually.
In 1952, astronomer Paul W. Merrill in California detected the spectral signature of technetium (in particular, light withwavelength of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type red giants.Sony VAIO VGN-BZ561P20 Battery
The stars were near the end of their lives, yet were rich in this short-lived element, meaning nuclear reactions within the stars must be producing it. This evidence was used to bolster the then-unproven theory that stars are where nucleosynthesis of the heavier elements occurs.Sony VAIO VGN-BZ562P Battery
More recently, such observations provided evidence that elements were being formed by neutron capture in the s-process.
Since its discovery, there have been many searches in terrestrial materials for natural sources of technetium.Sony VAIO VGN-BZ563P Battery
In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian Congo in extremely small quantities (about 0.2 ng/kg); there it originates as a spontaneous fission product of uranium-238. There is also evidence that the Oklonatural nuclear fission reactor produced significant amounts of technetium-99, which has since decayed into ruthenium-99.Sony VAIO VGN-BZAAFS Battery
Physical properties
Technetium is a silvery-gray radioactive metal with an appearance similar to that of platinum. It is commonly obtained as a gray powder. The crystal structure of the pure metal is hexagonal close-packed. Atomic technetium has characteristicemission lines at these wavelengths of light: 363.3 nm, 403.1 nm, 426.2 nm, 429.7 nm, and 485.3 nm.Sony VAIO VGN-BZAAHS Battery
The metal form is slightly paramagnetic, meaning its magnetic dipoles align with external magnetic fields, but will assume random orientations once the field is removed. Pure, metallic, single-crystal technetium becomes a type-II superconductorat temperatures below 7.46 K.Sony VAIO VGN-BZAANS Battery
Below this temperature, technetium has a very high magnetic penetration depth, the largest among the elements apart from niobium.
Chemical properties
Technetium is placed in the seventh group of the periodic table, between rhenium and manganese. Sony VAIO VGN-BZAAPS Battery
As predicted by periodic law, its chemical properties are therefore intermediate between those two elements. Of the two, technetium more closely resembles rhenium, particularly in its chemical inertness and tendency to form covalent bonds. Unlike manganese, technetium does not readily form cations (ions with a net positive charge).Sony VAIO VGN-CR11H/B Battery
Common oxidation states of technetium include +4, +5, and +7. Technetium dissolves in aqua regia, nitric acid, and concentrated sulfuric acid, but it is not soluble in hydrochloric acid of any concentration.
Hydride and oxides
Reaction of technetium with hydrogen produces the negatively charged hydride [TcH9]2? ion, which has the same type of crystal structure as (isostructural with) [ReH9]2?.Sony VAIO VGN-CR11S/L Battery
It consists of a trigonal prism with a technetium atom in the center and six hydrogen atoms at the corners. Three more hydrogens make a triangle lying parallel to the base and crossing the prism in its center. Although those hydrogen atoms are not equivalent geometrically, their electronic structure is almost the same.Sony VAIO VGN-CR11S/P Battery
This complex has a coordination number of 9 (meaning that the Tc atom has nine neighbors), which is the highest for a technetium complex. Two hydrogen atoms in the complex can be replaced by sodium (Na+) or potassium (K+) ions.
The metal form of technetium slowly tarnishes in moist air, and in powder form will burn in oxygen.Sony VAIO VGN-CR11S/W Battery
Two oxides have been observed: TcO2 and Tc2O7. Under oxidizing conditions, which tend to strip electrons from atoms, technetium(VII) will exist as the pertechnetate ion, TcO?
4.[20][24]
At temperatures of 400–450 °C, technetium oxidizes to form pale-yellow heptoxide:Sony VAIO VGN-CR11Z/R Battery
4 Tc + 7 O2 ? 2 Tc2O7
It adopts a centrosymmetric structure with two types of Tc-O bonds; their bond lengths are 167 and 184 pm, and the O-Tc-O angle is 180°.
Technetium heptoxide is the precursor to sodium pertechnetate:
Tc2O7 + 2 NaOH ? 2 NaTcO4 + H2O
Black-colored technetium dioxide (TcO2) can be produced by reduction of heptoxide with technetium or hydrogen.Sony VAIO VGN-CR120E/L Battery
Pertechnetic acid (HTcO4) is produced by reacting Tc2O7 with water or oxidizing acids, such as nitric acid, concentrated sulfuric acid, aqua regia, or a mixture of nitric and hydrochloric acids. The resulting dark red, hygroscopic (water absorbing) substance is a strong acid and easily donates protons. In concentrated sulfuric acid Tc(VII) tetraoxidotechnetate anion converts to the octahedral form of technetic(VII) acid TcO3(OH)(H2O)2.Sony VAIO VGN-CR120E/P Battery
The pertechnate (tetroxidotechnetate) anion TcO4? consists of a tetrahedron with oxygens in the corners and Tc atom in the center. Unlike permanganate (MnO4?), it is only a weak oxidizing agent. Pertechnate is often used as a convenient water-soluble source of Tc isotopes, such as 99mTc, and as a catalyst.Sony VAIO VGN-CR120E/R Battery
Sulfides, selenides, tellurides
Technetium forms various sulfides. TcS2 is obtained by direct reaction of technetium and elemental sulfur, while Tc2S7 is formed from the pertechnic acid as follows:
2 HTcO4 + 7 H2S ? Tc2S7 + 8 H2O
In this reaction technetium is reduced to Tc(IV) while exess sulfur forms a disulfide ligand.Sony VAIO VGN-CR120E/W Battery
The produced technetium heptasulfide has a polymeric structure (Tc3(µ3–S)(S2)3S6)n with a core similar to Mo3(µ3–S)(S2)62–.
Upon heating, technetium heptasulfide decomposes into disulfide and elementary sulfur:
Tc2S7 ? 2 TcS2 + 3 S
Analogous reactions occur with selenium and tellurium.Sony VAIO VGN-CR125E/B Battery
Clusters and organic complexes
Several technetium clusters are known, including Tc4, Tc6, Tc8 and Tc13. The more stable Tc6 and Tc8 clusters have prism shapes where vertical pairs of Tc atoms are connected by triple bonds and the planar atoms by single bonds.Sony VAIO VGN-CR13/B Battery
Every Tc atom makes six bonds, and the remaining valence electrons can be saturated by one axial and two bridging ligand halogen atoms such aschlorine or bromine.
Technetium forms numerous organic complexes, which are relatively well-investigated because of their importance for nuclear medicine.Sony VAIO VGN-CR13/L Battery
Technetium carbonyl (Tc2(CO)10) is a white solid. In this molecule, two technetium atoms are weakly bound to each other; each atom is surrounded by octahedra of five carbonyl ligands. The bond length between Tc atoms, 303 pm, is significantly larger than the distance between two atoms in metallic technetium (272 pm).Sony VAIO VGN-CR13/P Battery
Similar carbonyls are formed by manganese and rhenium.
A technetium complex[note 3] with an organic ligand (shown in the figure on right) is commonly used in nuclear medicine. It has a unique Tc-O functional group (moiety) oriented perpendicularly to the plane of the molecule, where the oxygen atom can be replaced by a nitrogen atom.Sony VAIO VGN-CR13/R Battery
Technetium, atomic number (Z) 43, is the lowest-numbered element in the periodic table that is exclusively radioactive. The second-lightest radioactive element, promethium, has an atomic number of 61. Atomic nuclei with an odd number of protons are less stable than those with even numbers, even when the total number of nucleons (protons + neutrons) are even.Sony VAIO VGN-CR13/W Battery
Odd numbered elements therefore have fewer stable isotopes.
The most stable radioactive isotopes are technetium-98 with a half-life of 4.2 million years (Ma), technetium-97 (half-life: 2.6 Ma) and technetium-99 (half-life: 211,000 years). Thirty other radioisotopes have been characterized with mass numbers ranging from 85 to 118.Sony VAIO VGN-CR131E/L Battery
Most of these have half-lives that are less than an hour; the exceptions are technetium-93 (half-life: 2.73 hours), technetium-94 (half-life: 4.88 hours), technetium-95 (half-life: 20 hours), and technetium-96 (half-life: 4.3 days).
The primary decay mode for isotopes lighter than technetium-98 (9843Tc) is electron capture, giving molybdenum (Z=42).Sony VAIO VGN-CR13G Battery
For heavier isotopes, the primary mode isbeta emission (the loss of an electron or positron), giving ruthenium (Z=44), with the exception that technetium-100 can decay both by beta emission and electron capture.
Technetium also has numerous nuclear isomers, which are isotopes with one or more excited nucleons. Technetium-97m (97mTc ; 'm' stands for metastability) is the most stable, with a half-life of 91 days (0.0965 MeV).Sony VAIO VGN-CR13G/B Battery
This is followed by technetium-95m (half-life: 61 days, 0.03 MeV), and technetium-99m (half-life: 6.01 hours, 0.142 MeV). Technetium-99m only emits gamma rays and decays to technetium-99.
Technetium-99 (9943Tc) is a major product of the fission of uranium-235 (23592U), making it the most common and most readily available Tc isotope.Sony VAIO VGN-CR13G/L Battery
One gram of technetium-99 produces 6.2×108 disintegrations a second (that is, 0.62 GBq/g).
Occurrence and production
Only minute traces occur naturally in the Earth's crust as a spontaneous fission product in uranium ores. A kilogram of uranium contains an estimated 1 nanogram (10?9 g) of technetium.Sony VAIO VGN-CR13G/P Battery
Some red giant stars with the spectral types S-, M-, and N contain an absorption line in their spectrum indicating the presence of technetium. These red-giants are known informally as technetium stars.
Fission waste product
In contrast with its rare natural occurrence, bulk quantities of technetium-99 are produced each year from spent nuclear fuel rods, which contain various fission products.Sony VAIO VGN-CR13G/R Battery
The fission of a gram of uranium-235 in nuclear reactors yields 27 mg of technetium-99, giving technetium a fission product yield of 6.1%. Other fissile isotopes also produce similar yields of technetium, such as 4.9% from uranium-233 and 6.21% from plutonium-239.Sony VAIO VGN-CR13G/W Battery
About 49,000 TBq (78 metric tons) of technetium is estimated to have been produced in nuclear reactors between 1983 and 1994, which is by far the dominant source of terrestrial technetium. Only a fraction of the production is used commercially.
Technetium-99 is produced by the nuclear fission of both uranium-235 and plutonium-239.Sony VAIO VGN-CR13T/L Battery
It is therefore present in radioactive waste and in the nuclear fallout offission bomb explosions. Its decay, measured in becquerels per amount of spent fuel, is dominant after about 104 to 106 years after the creation of the nuclear waste. From 1945 to 1994, an estimated 160 TBq (about 250 kg) of technetium-99 was released into the environment by atmospheric nuclear tests.Sony VAIO VGN-CR13T/P Battery
The amount of technetium-99 from nuclear reactors released into the environment up to 1986 is on the order of 1000 TBq (about 1600 kg), primarily by nuclear fuel reprocessing; most of this was discharged into the sea. Reprocessing methods have reduced emissions since then,Sony VAIO VGN-CR13T/R Battery
but as of 2005 the primary release of technetium-99 into the environment is by the Sellafield plant, which released an estimated 550 TBq (about 900 kg) from 1995–1999 into the Irish Sea. From 2000 onwards the amount has been limited by regulation to 90 TBq (about 140 kg) per year.Sony VAIO VGN-CR13T/W Battery
Discharge of technetium into the sea has resulted in some seafood containing minuscule quantities of this element. For example, European lobster and fish from west Cumbria contain about 1 Bq/kg of technetium.Sony VAIO VGN-CR15/B Battery
Fission product for commercial use
The vast majority of the technetium-99m used in medical work is produced by irradiating highly enriched uranium targets in a reactor, extracting molybdenum-99 from the targets, and recovering the technetium-99m that is produced upon decay of molybdenum-99.Sony VAIO VGN-CR150E/B Battery
Almost two-thirds of the world's supply comes from two reactors; the National Research Universal Reactor at Chalk River Laboratories reactor in Ontario, Canada, and the Petten nuclear reactor of the Netherlands. All major technetium-99m producing reactors were built in the 1960s and are close to the end of their lifetime.Sony VAIO VGN-CR190 Battery
The two new Canadian Multipurpose Applied Physics Lattice Experiment reactors planned and built to produce 200% of the demand of technetium-99m relieved all other producers from building their own reactors. With the cancellation of the already tested reactors in 2008 the future supply of technetium-99m became very problematic.Sony VAIO VGN-CR190E/L Battery
However the Chalk River reactor has been shut down for maintenance since August 2009, with an expected reopening in April 2010, and the Petten reactor had a 6-month scheduled maintenance shutdown beginning on Friday, February 19, 2010. With millions of procedures relying on technetium-99m every year,Sony VAIO VGN-CR190E/P Battery
the low supply has left a gap, leaving some practitioners to revert to techniques not used for 20 years. Somewhat allaying this issue is an announcement from a Polish research reactor, the Maria, that they have developed a technique to isolate technetium. The reactor at Chalk River Laboratory reopened in August 2010 and the Petten reactor reopened September 2010.Sony VAIO VGN-CR190E/R Battery
Waste disposal
The long half-life of technetium-99 and its ability to form an anionic species makes it a major concern for long-term disposal of radioactive waste. Many of the processes designed to remove fission products in reprocessing plants aim at cationic species like caesium (e.g., caesium-137) and strontium (e.g., strontium-90).Sony VAIO VGN-CR190E/W Battery
Hence the pertechnetate is able to escape through these treatment processes. Current disposal options favor burial in continental, geologically stable rock. The primary danger with such a course is that the waste is likely to come into contact with water, which could leach radioactive contamination into the environment.Sony VAIO VGN-CR19VN/B Battery
The anionic pertechnetate and iodide do not adsorb well onto the surfaces of minerals, so they are likely to be washed away. By comparison plutonium, uranium, andcaesium are much more able to bind to soil particles. For this reason, the environmental chemistry of technetium is an active area of research.Sony VAIO VGN-CR19XN/B Battery
An alternative disposal method, transmutation, has been demonstrated at CERN for technetium-99. This transmutation process is one in which the technetium (technetium-99 as a metal target) is bombarded with neutrons to form the short-lived technetium-100 (half-life = 16 seconds) which decays by beta decay to ruthenium-100.Sony VAIO VGN-CR20 Battery
If recovery of usable ruthenium is a goal, an extremely pure technetium target is needed; if small traces of the minor actinides such as americium and curiumare present in the target, they are likely to undergo fission and form more fission products which increase the radioactivity of the irradiated target.Sony VAIO VGN-CR21/B Battery
The formation of ruthenium-106 (half-life 374 days) from the 'fresh fission' is likely to increase the activity of the final ruthenium metal, which will then require a longer cooling time after irradiation before the ruthenium can be used.
The actual production of technetium-99 from spent nuclear fuel is a long process.Sony VAIO VGN-CR21E/L Battery
During fuel reprocessing, it appears in the waste liquid, which is highly radioactive. After sitting for several years, the radioactivity falls to a point where extraction of the long-lived isotopes, including technetium-99, becomes feasible. Several chemical extraction processes are then used, yielding technetium-99 metal of high purity.Sony VAIO VGN-CR21E/P Battery
Neutron activation
The metastable isotope technetium-99m is produced as a fission product from the fission of uranium or plutonium in nuclear reactors. Because used fuel is allowed to stand for several years before reprocessing,Sony VAIO VGN-CR21E/W Battery
all molybdenum-99 and technetium-99m will have decayed by the time that the fission products are separated from the major actinides in conventional nuclear reprocessing. The liquid left after plutonium–uranium extraction (PUREX) contains a high concentration of technetium asTcO?4 but almost all of this is technetium-99, not technetium-99m.Sony VAIO VGN-CR21S/L Battery
Molybdenum-99 can be formed by the neutron activation of molybdenum-98. Molybdenum-99 has a half-life of 67 hours, so short-lived technetium-99m (half-life: 6 hours), which results from its decay, is being constantly produced. The technetium can then be chemically extracted from the solution by using a technetium-99m generator ("technetium cow", also occasionally called a "molybdenum cow"). Sony VAIO VGN-CR21S/P Battery
By irradiating a highly enriched uranium target to produce molybdenum-99, there is no need for the complex chemical steps which would be required to separate molybdenum from a fission product mixture. This method requires that an enriched uranium target be irradiated with neutrons to form molybdenum-99 as a fission product, then separated.Sony VAIO VGN-CR21S/W Battery
A drawback of this process is that it requires targets containing uranium-235, which are subject to the security precautions of fissile materials.
Other technetium isotopes are not produced in significant quantities by fission; when needed, they are manufactured by neutron irradiation of parent isotopes (for example, technetium-97 can be made by neutron irradiation of ruthenium-96).Sony VAIO VGN-CR21Z/N Battery
Nuclear medicine and biology
Technetium-99m ("m" indicates that this is a metastable nuclear isomer) is used in radioactive isotope medical tests, for example as a radioactive tracer that medical equipment can detect in the human body.Sony VAIO VGN-CR21Z/R Battery
It is well suited to the role because it emits readily detectable 140 keV gamma rays, and its half-life is 6.01 hours (meaning that about 94% of it decays to technetium-99 in 24 hours). There are at least 31 commonly used radiopharmaceuticals based on technetium-99m for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors.Sony VAIO VGN-CR220E/R Battery
The longer-lived isotope technetium-95m, with a half-life of 61 days, is used as a radioactive tracer to study the movement of technetium in the environment and in plant and animal systems.
Industrial and chemical
Technetium-99 decays almost entirely by beta decay, emitting beta particles with consistent low energies and no accompanying gamma rays.Sony VAIO VGN-CR23/B Battery
Moreover, its long half-life means that this emission decreases very slowly with time. It can also be extracted to a high chemical and isotopic purity from radioactive waste. For these reasons, it is a National Institute of Standards and Technology(NIST) standard beta emitter, and is therefore used for equipment calibration.Sony VAIO VGN-CR23/L Battery
Technetium-99 has also been proposed for use in optoelectronic devices and nanoscale nuclear batteries.
Like rhenium and palladium, technetium can serve as a catalyst. For some reactions, for example the dehydrogenation of isopropyl alcohol, it is a far more effective catalyst than either rhenium or palladium. However, its radioactivity is a major problem in finding safe catalytic applications.Sony VAIO VGN-CR23/N Battery
When steel is immersed in water, adding a small concentration (55 ppm) of potassium pertechnetate(VII) to the water protects thesteel from corrosion, even if the temperature is raised to 250 °C. For this reason, pertechnetate has been used as a possible anodic corrosion inhibitor for steel, although technetium's radioactivity poses problems which limit this application to self-contained systems.Sony VAIO VGN-CR23/P Battery
While (for example) CrO42? can also inhibit corrosion, it requires a concentration ten times as high. In one experiment, a specimen of carbon steel was kept in an aqueous solution of pertechnetate for 20 years and was still uncorroded. The mechanism by which pertechnetate prevents corrosion is not well understood, but seems to involve the reversible formation of a thin surface layer.Sony VAIO VGN-CR23/R Battery
One theory holds that the pertechnetate reacts with the steel surface to form a layer of technetium dioxidewhich prevents further corrosion; the same effect explains how iron powder can be used to remove pertechnetate from water. (Activated carbon can also be used for the same effect.)Sony VAIO VGN-CR23/W Battery
The effect disappears rapidly if the concentration of pertechnetate falls below the minimum concentration or if too high a concentration of other ions is added.
As noted, the radioactive nature of technetium (3 MBq per liter at the concentrations required) makes this corrosion protection impractical in almost all situations.Sony VAIO VGN-CR240E/B Battery
Nevertheless, corrosion protection by pertechnetate ions was proposed (but never adopted) for use in boiling water reactors.
Precautions
Technetium plays no natural biological role and is not normally found in the human body. Technetium is produced in quantity by nuclear fission, and spreads more readily than many radionuclides.Sony VAIO VGN-CR240N/B Battery
It appears to have low chemical toxicity. For example, no significant change in blood formula, body and organ weights, and food consumption could be detected for rats which ingested up to 15 µg of technetium-99 per gram of food for several weeks.Sony VAIO VGN-CR290EAL Battery
The radiological toxicity of technetium (per unit of mass) is a function of compound, type of radiation for the isotope in question, and the isotope's half-life.Sony VAIO VGN-CR25G/N Battery
All isotopes of technetium must be handled carefully. The most common isotope, technetium-99, is a weak beta emitter; such radiation is stopped by the walls of laboratory glassware. The primary hazard when working with technetium is inhalation of dust;Sony VAIO VGN-CR290EAN Battery
such radioactive contamination in the lungs can pose a significant cancer risk. For most work, careful handling in a fume hood is sufficient; a glove box is not needed.Sony VAIO VGN-CR290EAP Battery,Sony VAIO VGN-CR290EAR Battery,Sony VAIO VGN-CR290EAW Battery,
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